With all due respect what you're suggesting is incredibly Anti-American. Freedom of Speech gives people the right to post offensive statements whether you think it's appropriate or not. And lacks manners? OMG, really who are you to judge something like this?
First of all, the first logical fallacy in this is the absolutism of the first amendment, the SCOTUS has already ruled that certain speech is NOT protected, like fighting words, incitement to riot, obscenity, libel, and defamation, you are taking an absolutist stance. Secondly, attacking people's core beliefs right next to a symbol of their core beliefs can be seen as an attack(fighting words) and if said people who felt attacked decided to riot, the onus would most likely be on those who started it, that is, the people who put an atheist slogan right next to a manger scene(incitement to riot), so, it could be seen by those who felt attacked and law enforcement as unprotected speech under the correct circumstances. Third, why attack people in that manner, anyone who believes in decency could make the call you are questioning, who are YOU to judge people's opinions?
I think the sign is offensive too but I will defend their right to display as I would anyone who is legally expressing Freedom of Speech.
It was in horrendous taste and the people who put it up should be ashamed of themselves.
What you are suggesting is that you want to censor things that are offensive and bad manners which is totally and completely illegal according to the Constitution of the United States. I'm guessing that upon further consideration you do not truly think the sign should be taken down, right?
See the first response.